1. Field of the Invention
The present invention relates to an optical device having a lens barrel for holding an optical system, and a casing for housing the lens barrel. The casing has two casing sections that are movable relative to each other, and a distribution cable is provided between the casing sections.
2. Description of the Related Art
As an example of the optical device, there is a slide-type binocular telescope, which has a casing composed of two casing sections slidably engaged with each other so as to expand and contract in right and left directions, and in which an observation optical system is housed in each of the casing sections. The casing sections are moved relative to each other, so that the interpupillary distance can be adjusted, which is a necessary function for a binocular telescope. Although an electronic control device is not essential in the slide-type binocular telescope, if the binocular telescope is provided with an automatic focusing function or an electronic photographing function, an electronic control device should be provided.
As another example of the optical device, there is an electronic camera, i.e., digital camera using a solid-state imaging device. For a digital camera, it is important to be compact and portable, and therefore, a part of the casing may be able to expand and contract relative to the main part of the casing. Namely, when carrying the digital camera, a part of the casing is housed in the main part of the casing so as to reduce the overall dimensions of the body, and when performing a photographing operation, the part of the casing housed in the main part is pulled. Of course, an electronic control device is essential for a digital camera.
In the optical devices described above, a battery and a power supply circuit board are essential in order to supply electric power to the electronic control devices. Namely, a power supply circuit provided on the power supply circuit board receives a power supply, and supplies electric power. having a predetermined voltage to electronic parts contained in the electronic control device.
When the battery and the power supply circuit board are disposed at separate positions, or at opposite sides of the binocular telescope or the digital camera, it is necessary to connect the battery and the power supply circuit board with a power supply cable, which extends between the two casing sections that are movable relative to each other. Thus, to ensure the relative movement of the casing sections, the power supply cable should be long enough. Namely, the power supply cable should be provided with enough looseness or slackness, and be deformed smoothly in accordance with the relative movement of the casing sections. In this case, the movement of the power supply cable should be restrained so as not to interfere with the internal mechanism provided in the binocular telescope or digital camera. However, provision of a restraining mechanism for properly restraining the movement of the power supply cable will increase the cost and size of the binocular telescope or digital camera, and therefore, is not preferable.
In the optical device described above, the relationship between the battery and the power supply circuit board was explained. On the other hand, in another type of optical device in which two casing sections are provided with control circuit boards, a signal cable should be provided between the control circuit boards, and hence, there occurs the same problem as described above.
Therefore, an object of the present invention is to provide an optical device in which a movement of a distribution cable is properly controlled, when two casing sections are moved relative to each other, and to achieve this without incurring an additional manufacturing cost.
According to the present invention, there is provided an optical device comprising a lens barrel, a casing, and a distribution cable. The lens barrel holds an optical system. The lens barrel is housed in the casing. The casing has two casing sections that are movable relative to each other. The distribution cable extends between the casing sections. The distribution cable is loosely wound around the lens barrel, whereby a movement of the distribution cable, caused by a relative movement of the casing sections, is absorbed by the loosely wound portion of the distribution cable.
A pair of the lens barrels may be housed in the casing sections, and in this case, the distribution cable is wound around one of the pair of lens barrels. Further, in this case, a pair of observation optical systems, functioning as a binocular telescope, may be provided, and at least a part of the observation optical systems may be held by the pair of lens barrels. The two casing sections may also be moved relative to each other to adjust the interpupillary distance of the pair of observation optical systems. Furthermore, in this case, the two casing sections may be linearly movable relative to each other in such a manner that the optical axes of the pair of observation optical systems are moved in a predetermined plane, so that the interpupillary distance of the pair of observation optical systems can be adjusted.
Each of the pair of observation optical systems may comprise an objective optical system, an erecting optical system, and an ocular optical system, only the objective optical system being housed in the lens barrel, the erecting optical system and the ocular optical system being movable back and forth relative to the objective optical system to perform a focusing movement. Preferably, one of the casing sections is provided with a focusing mechanism and a rotary wheel for operating the focusing mechanism to perform the focusing movement, and the distribution cable is wound around the lens barrel housed in another of the casing sections. Preferably, the rotary wheel is an annular projection formed on an outer surface of a rotary wheel cylinder in which a photographing optical system is mounted. Optionally, a battery is housed in an outer side of one of the casing sections, and a power supply circuit board is housed in an outer side of another of the casing sections, the distribution cable being a power supply cable connecting the battery and the power supply circuit board.
Preferably, the distribution cable has a loop portion that is loosely wound around the lens barrel, the movement of the distribution cable being absorbed by a change in the diameter of the loop portion. The loop portion may keep the loop shape without contacting an inner wall of the casing when the casing sections are relatively positioned such that the diameter of the loop portion reaches its maximum.